Hinokitiol plus fluconazole: potent inhibitory efficacy on Candida species resistant to azole

Nikaein, Donya; Shokri, Hojjatollah; Sharifzadeh, Aghil; Mohammadian, Mohammadreza; Jahanian, Ahmad

doi:10.22034/cjvs.2026.560426.1052

Hinokitiol plus fluconazole: potent inhibitory efficacy on Candida species resistant to azole

Document Type : Original Article

Authors

Donya Nikaein ¹

Hojjatollah Shokri ²

Aghil Sharifzadeh ¹

Mohammadreza Mohammadian ³

Ahmad Jahanian ¹

¹ Department of Microbiology and Immunology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.

² Department of Pathobiology, Faculty of Veterinary Medicine, Amol University of Special Modern Technologies, Amol, Iran.

³ Department of Animal and Poultry Health and Nutrition, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.

10.22034/cjvs.2026.560426.1052

Abstract

Candida species represent the most prevalent types of yeasts affecting humans and animals. The increase in antifungal resistance has raised the issue of using these medications in tandem to improve treatment outcomes. Guided by the CLSI M27-A3 guideline, this investigation quantified the synergistic potential of hinokitiol and fluconazole against Candida albicans, C. tropicalis, C. glabrata, and C. krusei. The primary metrics for this assessment were the minimum inhibitory and fungicidal concentrations (MICs and MFCs), which were established using a broth microdilution methodology. Using data from a checkerboard microdilution test, we calculated the fractional inhibitory concentration indices (FICIs) to evaluate the interaction between hinokitiol and fluconazole. A strong synergistic interaction between hinokitiol and fluconazole was evident in every tested isolate (100%) of fluconazole-resistant C. albicans and C. glabrata. The corresponding FICI values, falling within ranges of 0.304–0.498 and 0.290–0.492, respectively, confirm this robust synergistic activity. This activity was noted against a background of universal fluconazole resistance, with hinokitiol alone showing MIC values from 0.81 µg/ml (C. glabrata) to 6.9 µg/ml (C. krusei). FICI scores spanning 0.500 to 0.750 for every C. krusei strain (100%) confirm a strictly additive pharmacological interaction between hinokitiol and fluconazole. Additionally, the FICI values for the combination of hinokitiol and fluconazole for C. tropicalis strains varied from 0.245 to 0.730, demonstrating a synergistic effect in 13 (86.7%) strains and an additive effect in 2 (13.3%) strains. This study suggests that hinokitiol may help reduce fluconazole dosages and inhibit the development of fluconazole-resistant Candida species

Keywords

Candida

Fluconazole

Hinokitiol

Synergy

Subjects